A Bacterial Disease of Sto^e Fruits 413 



culture media, but the injury was also far less marked when it was 

 inoculated on the green tissues of the different hosts. In the fall of 1911 

 Abundance plum twigs were inoculated with cultures of this strain, and in 

 the summer of 1912 the organism was regained from one of the twigs. 

 The culture was again grown continuously on a Hiss-glucose medium. 

 The regained culture made a shghtly better growth on the various media 

 than did the culture which had been growing continuously on the Hiss- 

 glucose medium, and was also slightly more aggressive when inoculated 

 on the green tissues; but it was far less virulent than when first ol^tained. 

 In the sunnner of 1912 the four old strains which had been growing con- 

 tinuously on the Hiss-glucose medium since 1910 were rejuvenated by 

 growing them in bouillon for fifteen days, maldng transfers to a new 

 medium every third daj^ and finally on the fifteenth day all were again 

 placed on the Hiss-glucose medium. The plum organism at once became 

 again the most ^dgorous grower, and when inoculated on peach leaves and 

 twigs it was also the most aggressive. From these results it appears that 

 vigor is the controlling factor in the \arulence of the organism. 



Grou-p mimher. — The group number, according to the descriptive 

 chart of the Society of American Bacteriologists, is 211.2232523. 



Life history 



Inoculation. — Bacterium Pruni, so far as is known, passes its entire 

 life cycle in nature within the tissue of the host. The disease usually 

 makes its appearance in the spring shortly after .the leaves have mifolded, 

 but as a rule serious outbreaks do not occur before May and often not 

 until later. Cankers on the twigs and limbs are the principal sources of 

 infection in the spring. Trees bearing t-^dgs on which inoculations result 

 in the development of well-formed cankers, are mvariably the fu'st to 

 develop leaf spot abundantly the following year. Young trees which 

 suffer severely from repeated outbreaks of the shot-hole condition usually 

 show many twig cankers.. Twig cankers are also constantly associated 

 with the early spring outbreaks on older trees. The tissues of the bud 

 may likewise become invaded, and a~e often responsible for the early 

 spring infection. Eleven out of fifty cultures made from the centers of 

 buds taken in August from peach twigs on which the foliage was badly 

 shot-holed, yielded manj- colonies of the yellow organism. 



